I am looking for a good wide angle zoom and I think it is down between a couple and wanted to check and see if anyone had any feedback on them. The first is the Tamron SP AF 17-35mm F2.8-4 DI LD, and the second is the Sigma 18-50 F2.8 EX DC. I want to use it on both my digitals and film cameras. Any comments or suggestions would be greatly appreciated.